In a conventional Integrated Fan-Out (InFO) process, a top package, in which a first device die is bonded, is bonded to a bottom package. The bottom package may also have a device die packaged therein. By adopting the InFO process, the integration level of the packages is increased.
In an existing InFO process, the bottom package is formed first, which includes encapsulating a molding compound on a device die and a plurality of through-molding vias. Redistribution lines are formed to connect to the device die and the through-molding vias. A top package, which may include device dies bonded to an additional package substrate, is then bonded to the bottom package. A multi-stack package (sometimes referred to herein as a “MUST package”) is a package with two or more levels of multiple semiconductor devices (sometimes referred to as “chips” or “dies”), and may be formed by repetition of the InFO process.